where \(a\)  and \(b\)  are positive environment-related parameters and \(\theta \)  is the elevation angle between the UAV and the ground devices (controller or robot) as shown in Fig. REF . Some typical values of \(a\)  and \(b\)  can be found in Table I of [1]}. It is observed from (REF ) that the LoS probability increases with the elevation angle, which is reasonable as the probability that signal is blocked is decreasing when the height of UAV is increasing.
